We will carry out experiments on the circadian rhythm in the eye of Aplysia and on the circadian rhythm of behavioral activity. Experiment 1: We will attempt to locate the red sensitive extraocular photoreceptors which are known to entrain the eye rhythm. Experiment 2: We wish to find if freerunning oscillators outside the eye can influence the phase of the eye clock. Experiment 3: We wish to see if water turbulence, which inhibits locomotor movements, also can be a zeitgeber for the behavioral rhythm and the eye clock. Experiment 4: We would like to know whether stimulation of the rhinophore nerve, which inhibits the photic response of the eye, can also reset the ocular clock. BIBLIOGRAPHIC REFERENCES: Smith, J.T. & Lickey, M.E. Long term recording from Neuron R15 in Aplysia does not reveal circadian rhythm, Fed. Proc. 1976: (Abstr.) In press. Lickey, M.E.; Block, G.D.; Hudson, D.J.; & Smith, J.T. Circadian Oscillators and photoreceptors in the Marine Gastropod Aplysia. Photochem. & Photobiol., 1976.